Phase behavior and phase structure of a cationic fluorosurfactant in water

The phase behavior of the cationic fluorocarbon surfactant 1,1,2,2-tetrahyd roperfluorodecylpyridinium chloride in water has been studied using small-a ngle X-ray and H-2 NMR spectroscopy as the main techniques. The following p hase sequence was found: micellar (L-1), hexagonal (H-I), centered rectangu lar (R; spacegroup c2mm) and centered trigonal (T, spacegroup R (3) over ba r m) with increasing surfactant concentration. At higher concentrations evi dence for random mesh phase and a lamellar phase was found, at high tempera tures a bicontinuous cubic phase was found. Compared to a cationic hydrocar bon surfactant of similar hydrophobicity, the occurrence of the intermediat e phases is more extensive in the phase diagram, and the fluorocarbon surfa ctant prefers to form intermediate phases instead of a cubic phase. The sur face curvature of the aggregates changes from highly curved cylindrical str uctures of the hexagonal phase to the planar bilayer structure of the lamel lar phase over a sequence of geometries that allow the average of the mean curvature to change gradually as water content is decreased.